Process of production of mixtures of gases hard to liquefy



Aug. 18, 1942. I ETIENNE v PROCESS or raonub nokor MIXTUR S OF GASESHARD TO LIQUEFY 1-11'1& June 12, 1940 MLM'M Patented Aug. 18, 1942PROCESS OF PRODUCTION OF MIXTURES OF GASES HARD TO LIQUEFY AlfredEtienne, Paris, France, assignor to lAir Liquide, Socit Anonyme pourlEtude et lExploitation des Procds Georges Claude,

Paris, France Application June 12, 1940, Serial No. 340,167 In FranceJuly 19, 1939 12 Claims.

This invention relates to the production of mixtures ofdimcultly-liqueflable gases. one of which at least is obtained byliquefylng a gaseous mixture. One feature of the invention is that it isapplicable to the production of nitrogenhydrogen mixtures such as are tobe utilized for ammonia synthesis and which must, as known,

consist of one volume of nitrogen for three volumes of hydrogen. For thepurpose of simplifying the following explanations, the production ofsuch nitrogen-hydrogen mixtures will be referred to, but it is to beunderstood that the invention is also applicable inter alla to theproduction of mixtures of other liqueflable gases, such as carbonmonoxide-hydrogen mixtures which, for instance, are to be utilized forthe synthesis of organic compounds, as methyl alcohol.

In order to prepare, by partial liquefaction from coke oven or othersimilar gases, the nitrogen-hydrogen mixtures to be utilized for ammoniasynthesis, it has been proposed to carry out the partial liquefaction ofthe coke oven gas and its final washing with liquid nitrogen under suchtemperature and pressure conditions that the obtained mixture, whichconsists of nitrogen and hydrogen, has the composition N+H3, which isnecessary for ammonia synthesis, but generally such temperature andpressure conditions cannot practically be made to prevail at the samtime in economic manner, and the final gaseous mixture generallycontains less than one volume of nitrogen for three volumes of hydrogen.In order to obtain a gaseous mixture having the composition N-l-H3, thenecessary makeup nitrogen is accordingly added to the final gaseousmixture. This addition of nitrogen is accompanied by no substantialthermal effect.

On the other hand, when obtaining mixtures of nitrogen and hydrogen,starting from coke oven gas, it has already been proposed to compressthe coke oven gas, to cool it so as to separate therefrom, byliquefaction, the greater portion of the constituents other thanhydrogen, to expand, with performance of external work, the gaseouseiiluent of the liquefaction, and to put the expanded gas into contactwith liquid nitrogen. The liquid nitrogen vaporises in the expanded gasto give a resultant mixture of nitrogen and hydrogen. If the expandedgas is free from carbon monoxide, the liquid nitrogen is added in such asmall quantity that it can wholly vaporise in the expanded gas. If, onthe contrary, the expanded gas still contains carbon monoxide, theliquid nitrogen is added in greater quantity and the non-vaporisedportion of the liquid nitrogen is utilized for washing the expanded gasso as to free it from its carbon monoxide. In both cases, if theobtained mixture of nitrogen and hydrogen contains less than one volumeof nitrogen for three volumes of hydrogen, which will generally be thecase, there must be subsequently added thereto th quantity of nitrogenin gaseous state which is necessary for obtaining a mixture of hydrogenand nitrogen suitable for ammonia synthesis.

In the process according to this invention, the hydrogen (or moregenerally a first diificultlyliqueflable gas resulting from theseparation of a gaseous mixture by liquefaction) is admixed withnitrogen (or a second gas hard to liquefy). namely under such conditionsthat a useful thermal efiect is brought about.

The process according to the present invention for producing mixtures ofdiflicultly-liquefiable gases consists in cooling a gaseous mixture,liquefying it so as to separate therefrom a first gas which is to becomea constituent of the gaseous mixture to be produced, cooling a secondgas which is also to become a constituent of the gaseous mixture to beproduced, mixing the less volatile of these two constituents, in theliquid state, with the other constituent in the gaseous state, theconstituent in the liquid state being at a temperature sufiiciently lowand being of suiliciently great quantity, that at least a portion ofsaid liquid constituent does not vaporise when the addition takes place,and maintaining the mixture of gas and liquid thus constituted in heatexchange relation to the gases to be cooled, for instance, the treatedgaseous mixture, so that there is an exchange of heat from the gases tobe cooled to the liquid and gaseous mixture, such exchange of heattaking place either at the end of the purification of the gaseousmixture during the course of its treatment.

When applied to the production of nitrogenhydrogen mixtures of the kindreferred to above, the process consists in cooling the gaseous nitrogen,liquefying it and admixing it while in its liquid state with gaseoushydrogen, the liquid nitrogen being at so low a temperature and in sogreat a quantity that at least a portion of the liquid nitrogen does notvaporise at the time of the addition. The mixture of gas and liquid thusiconstituted is then warmed up, its cold being mixture, of which it is apart, the temperature which corresponds to the partial pressure oi thenitrogen in the gaseous phase, which temperature constantly remainslower than the temperature which the nitrogen (or the less volatile gas)would have if it would vaporise alone under the pressure of the mixture.By thus vaporising the liquid nitrogen in the hydrogen it is possible toobtain the favorable eifect of a lowering of temperature in the colderregion of the separating apparatus.

From the place where the liquid nitrogen and the gaseous hydrogen (orthe gas and the liquid) are mixed, no further purification ofthe'mixture by partial condensation can take place. Therefore, it isimportant that the formed mixture be free from obnoxious impurities.Thus, if one is concerned with the production of a N-i-Ha mixturesubstantially free from carbon monoxide, it will generally be necessaryto wash, in known manner, with liquid nitrogen the gaseous effluent ofthe partial liquefaction of the coke oven gas before adding thereto themakeup nitrogen in the liquid state.

The process of the invention will be described hereinafter by way ofexample in the special case above referred to, that is, where one isconcerned with producing from coke oven gas a gen introduced through thepipe G is in quantity. suiiiciently great and at a temperaturesuiiiciently low that at least a portion thereof remains in the liquidstate in the gaseous mixture to which it is added. It is the resultingmixture of liquid nitrogen and of gas from the expansion engine F whichflows around the external tubes C while subjecting them to the abovementioned cooling. After having been warmed up by contact with thesetubes, the mixture passes out through the pipe H.

In certain cases it may happen that the amoun of liquid nitrogencondensed in the pipes C is mixture of nitrogen and hydrogen of the'commixture is still under the initial pressure to which the coke ovengas has been compressed.

In Fig. 1, coke oven gas, which has previously been cooled in heatexchangers, not shown, and stripped by partial liquefaction of itsethylene, the greater part 01' its methane, and possibly of a portion ofits carbon monoxide, rises through the washing column A, in which it iswashed by pure liquid nitrogen. The substantially pure mixture ofnitrogen and hydrogen obtained at the top of the column A passes throughthe pipe B to a nest of tubes 0, closed at their upper end. These tubesare cooled externally, in a manner which will be described later, tosuch an extent that nitrogen condenses therein. It is this liquidnitrogen which is conveyed through the pipe D to the top of the washingcolumn A. From the top of the closed tubes C, the nitrogen-hydrogenmixture flows downward through the open-ended tubes E located inside thetubes C and is warmed by indirect contact with the gas rising in thetubes C. From the lower end of the tubes E, the nitrogen-hydrogenmixture is passed to an expansion engine F, in which it expands withproduction of external work, and with resultant lowering of itstemperature. Liquid nitrogen under pressure is conveyed through the pipeG, expanded through the valve T to the pressure of the expandedhydrogen-nitrogen mixture and added thereto. The liquid ,nitrogenintroduced through the pipe G previously has been cooled to a lowtemperature by heat exchange with the products resulting from theseparation of coke oven gas intotits constituents, and is in suchquantity that the mixture resulting from its union with the expandedmixture of hydrogen and nitrogen has substantially the composition ofN+H:. Under these conditions, the liquid nitrotoo small to accomplish asatisfactory washing of the coke-oven gases in the column A. In suchcases supplementary liquid nitrogen will then be introduced into thecolumn A through the pipe U at the top thereof.

In Fig. 2, the compressed coke oven gas, which has previously beencooled under the same conditions as in the case of Fig. 1, and whichstill contains an important proportion of carbon monoxide, flowsupwardly successively through a washing column P, a nest of tubes S anda second washing column A. In the column P, the compressed gas is washedwith liquid nitrogen still containing some carbon monoxide and isstripped only incompletely of its carbon monoxide, in the nest of tubes8 it is cooled as will be mentioned hereinafter. Such cooling of thecompressed gas in the tubes 8 brings about a partial condensation of thegas. In the washing column A the uncondensed gas is washed with pureliquid nitrogen, conveyed to the column through the pipe K, which takesup in known manner the small.quantities of carbon monoxide which remainin the gaseous mixture. The liquid nitrogen flows downwardlysuccessively through the column A, the nest of tubes S and the column P,thereby growing richer in carbon monoxide. On the other hand, in anapparatus not shown, nitrogen is compressed and brought to a lowtemperature in liquid state by being put in heat exchange with theproducts resulting from the separation of the coke oven gas into itsconstituents. The cold liquid nitrogen thus obtained enters the pipe Xand is divided into two parts. One part passes through the exchanger Mwhere it is cooled, and is expanded through the valve R and constitutesthe aforementioned washing liquid nitrogen which is introduced to theupper end of column A through the pipe K. The other part passes throughthe pipe G, is expanded through the valve T and is added to thesubstantially pure hydrogen-nitrogen mixture which results from thewashing operation carried out in the column A, and which leaves throughthe pipe L. This second portion of liquid nitrogen is in such quantitythat the obtained mixture of gas and liquid has substantially thecomposition N-l-Ha. The mixture of liquid and gas thus formed flowsthrough the exchanger M, in which it cools the liquid nitrogen deliveredat the top of the column A through the pipe K. When leaving theexchanger M, the nitrogen-hydrogen mixture, still containing some liquidand still under pressure, is passed through the pipe N around the nestof tubes S, where it cools the gaseous mixture rising through saidtubes, and leaves through the pipe 0 after being wholly or partiallyvaporized.

A portion of the nitrogen contained in the gaseous mixture risingthrough the nest of tubes 8 liquefles and unites with the liquidnitrogen descending from the column A. The production of. cold isobtained, for instance, by means of a nitrogen cycle.

In the example of Fig. 2, the cooling of the liquid nitrogen in theexchanger M could in certain cases be suppressed.

The liquid mixture of carbon monoxide and nitrogen resulting from theseparation of the coke oven gas into its constituents is preferablyutilized as the medium for the cooling of the compressed nitrogen whichis to constitute the make-up liquid nitrogen in the two examples givenabove. But the gaseous mixture of hydrogen and nitrogen obtained as theother product of the separation of the coke oven gas into itsconstituents could also be so utilized. In that case, the mixture ofhydrogen and nitrogen will preferably be partly warmed before beingutilized for cooling the nitrogen; As to the preliminary cooling of thenitrogen, it is obtained either by putting compressed nitrogen in 'heatexchange with the separation products and especially the liquid methane,or by directly expanding the compressed nitrogen, at the surroundingtemperature, or after being partially cooled, to an intermediatepressure which permits its liquefaction by heat exchange with the coldseparation products.

The origin of the make-up nitrogen utilized in the liquid state in thetwo above examples is immaterial. The 'nitrogen can, for example, beobtained by rectifying the liquid mixture of nitrogen and carbonmonoxide obtained by cooling and washing the coke oven gas, and warmingup the gaseous nitrogen resulting from this rectification in order tocompress it at the surrounding temperature.

It has been assumed in the foregoing that the starting gaseous mixtureis coke oven gas, but the process would still be applicable, unaltered,if the starting gas were water-gas or. any other similarhydrogen-containing gaseous mixture. Again, the process according to theinvention may be applied to the obtention of hydrogencarbon monoxidemixtures by partial liquefaction of hydrogen-containing gaseousmixtures. In that case the washing of the gas with liquid nitrogen will,of course, be dispensed with and there will be obtained a gaseousmixture consisting of hydrogen and a little carbon monoxide andnitrogen, to which carbon monoxide will be added in the liquid state.More generally, the process is applicable to the production of mixturesof diflicultly-liquefiable gases, one of which at least is obtained bythe separation of a gaseous mixture by liquefaction.

I claim:

1. A process for producing mixtures of difficultly-liquefliable gasescontaining a constituent of greater volatility and a constituent of lessvolatility which comprises cooling a gaseous mixture containing theconstituent of greater volatility sufficiently to separate saidconstituent from other constituents of the gaseous mixture byliquefaction, mixing said separated constituent, in the gaseous state,with the constituent of less volatility, in the liquid state, theconstituent of less volatility being in an amount sufficiently great andat a temperature sufficiently low that at least a portion thereof is notvaporized when added to the more volatile constituent in the gaseousstate, and passing the resultant mixture of gas and liquid into heatexchange relation with the first-mentioned gaseous mixture to cool saidfirst-mentioned gaseous mixture and to cause the liquid of theliquid-and-gas mixture to be vaporized.

2. A process for the production of diiilcultlyliquefiable gases as setforth in claim 1, in which the heat exchange between the resultingmixture of gas and liquid and the first-mentioned gaseous mixture takesplace at the end of the cooling of the first-mentioned gaseous mixtureto separate the constituent of less volatility.

3. A process for the production of difficultlyliquefliable gases as setforth in claim 1, in which the heat exchange between the resultingmixture of gas and liquid and the first-mentioned gaseous mixture takesplace at an intermediate stage of the cooling of the first-mentionedgaseous mixture to separate'the constituent of less volatility. 4. A.process for producing mixtures of hydrogen and nitrogen having thecomposition N-i-Hz which comprises washing a gaseous mixture containinghydrogen with liquid nitrogen, mixing the resulting gaseous mixturecontaining hydrogen and nitrogen, in the gaseous state, with liquidnitrogen, the amount of admixed liquid nitrogen being sufficiently greatand its temperature sumciently low that at least a portion thereof isnot vaporized when added to the gaseous mixture containing hydrogen andnitrogen, andpassing the resulting mixture of gas and liquid into heatexchange relation with the gaseous mixture resulting from the washing ofthe first-mentioned gaseous mixture with liquid nitrogen to. cool it andto cause the liquid of said liquid-aAd-gas mixture to be vaporized.

5. A process for producing mixtures of hydrogen and nitrogen having thecomposition N-I-I-h which comprises washing a gaseous mixture containinghydrogen with liquid nitrogen, subjecting the resulting gaseous mixturecontaining hydrogen and nitrogen to cooling sufficient to liquefy atleast part of the nitrogen thereof, mixing the remainder of the mixture,in the gaseous state, with liquid nitrogen, the amount of admixed liquidnitrogen being sufiiciently great and its temperature sufficiently lowthat at least a portion thereof is not vaporized when added to saidremainder of the mixture, and passing the resulting mixture of gas andliquid into heat exchange relation with the gaseous mixture resultingfrom the washing of the first-mentioned gaseous mixture with liquidnitrogen to cool it and to cause the liquid of said liquid-and-gasmixture to be vaporized.

6. A process for producing mixtures of hydrogen and nitrogen having thecomposition N+Ha which comprises washing a gaseous mixture containinghydrogen with liquid nitrogen, mixing the resulting gaseous mixturecontaining hydrogen and nitrogen, in the gaseous state, with liquidnitrogen, the amount of admixed liquid nitrogen being sufliciently greatand its temperature sufficiently low that at least a portion thereof isnot vaporized when added to the gaseous mixture containing hydrogen andnitrogen, and passing the resulting mixture of gas and liquid into heatexchange relation with the first-mentioned gaseous mixture while it isbeing washed with the liquid nitrogen to cool said first-mentionedgaseous mixture and to cause the liquid of said liquid-and-gas mixtureto be vaporized.

7. A process for the production of mixtures of hydrogen and nitrogen asset forth in claim 4, in which the liquid nitrogen used for washing thefirst-mentioned gaseous mixture is cooled by heat exchange with saidliquid-and-gas mixture.

8. A process for producing a mixture of lowboiling gases which comprisespartially liqueiying being in an amount sumciently great and at a atemperature suniciently low that at least a porthereoi is not vaporizedwhen added to the gaseous efliuent 01! said partial liquefaction, and

passing the resultant mixture of gas and liquid into heat exchangerelation with the mixture of gases to be partially liquefied.

9. A process for producing a mixture of hydrogen and nitrogen whichcomprises cooling a hydrogen-containing gaseous mixture sui'iiciently topartially liquei'y it, washing the non-liquid por tion of saidgaseousmixture with liquid nitrogen, mixing the gases resulting fromsaid washin operation with a further quantity of liquid nitrogen,saidiurther quantity of liquid nitrogen being in an amount sumcientlygreat and at a temperature suiliciently low that at least a portionthereof is not vaporized when added to the gases from said washingoperation, and passing the resultant mixture of gas and liquid into heatexchange relation with the gases to be partially liquefied. 10. Aprocess for producing a mixture of hydrogen and nitrogen which comprisescooling a hydrogen-containing gaseous mixture sufllciently to partiallyliquefy it, washing the non-liquid portion of said gaseous mixture withliquid nitrogen, mixing the gases resulting from said washing operationwith a further quantity of liquid nitrogen, said further quantity ofliquid nitrogen being in an amount sufllciently great and at atemperature sufllciently low that at least a portion thereof is notvaporized when added to the gases from said washing operation, andpassing the resultant mixture of gas and liquid into heat exchangerelation to the non-liquid portion oi the gases resulting from. thepartial liquefaction of the hydrogen-containing gaseous mixture whilesaid non-liquid portion is being subjected to the washing with liquidnitrogen.

11. A process for producing a mixture 01' hydrogen and nitrogen whichcomprises cooling 9. hydrogen-containing gaseous mixture suiliciently topartially liquefy it, washing the non-liquid portion of said gaseousmixture with liquid nitrogen, turther'cooling the washed gases, expanding said washed gases with external work, mixing the expanded gases withliquid nitrogen, said last-mentioned liquid nitrogen being in an amountsufllciently great and at a temperature suiiiciently low that at least aportion thereof is not vaporized when it is added to the expanded gases,and passing the resulting mixture of gas and liquid into heat exchangerelation with the washed gases which are to be further cooled.

12. A process for producing a mixture of hydrogen and nitrogen whichcomprises cooling 9. hydrogen-containing gaseous mixture sufficiently topartially liqueiy it, washing the non-liquid portion of said gaseousmixture with liquid nitrogen, mixing the gases resulting from saidwashing operation with a further quantity of liquid nitrogen, saidfurther quantity of liquid nitrogen being in an amount suilicientlygreat and at a temperature sufliciently low that at least a portionthereof is not vaporized when added to the gases from said washingoperation, and passing the resultant mixture of gas and liquid into heatexchange relation first with said washing liquid nitrogen and then withthe non-liquefied portion of the hydrogen-containing gaseous mixturewhile said non-liquid portion is being subjected to the washing withliquid nitrogen.

ALFRED ETIENNE.

